Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $135.26   11.786%   $151.2017   $151.20   $151.20   $151.20  
  Purchase #2 $246.97   4.568%   $258.2516   $258.25   $258.25   $258.30  
  Purchase #3 $39.66   4.676%   $41.5145   $41.51   $41.50   $41.50  
  Purchase #4 $49.78   11.744%   $55.6262   $55.63   $55.65   $55.60  
  Purchase #5 $195.57   9.451%   $214.0533   $214.05   $214.05   $214.10  
  Purchase #6 $184.57   4.707%   $193.2577   $193.26   $193.25   $193.30  
  Purchase #7 $125.30   4.341%   $130.7393   $130.74   $130.75   $130.70  
  7 purchase totals = $977.11       $1,044.6443   $1,044.64   $1,044.65   $1,044.70